1. Field of the Invention
This invention relates to a compact projection device which is suited for use with a copying machine of the slit exposure type and which is free of irregurality of exposure.
2. Description of the Prior Art
In the conventional projection device of a copying machine or the like, the projection lens system has comprised a single ocellar lens and due to the limitation of the angle of view taking the depth of focus into account, the conjugate from the surface of an object to the image plane has been long and this has necessarily led to a problem that the device is bulky. To eliminate such problem, there is known a projection device in which the projection lens system is formed by an ommateal lens having the same angle of view as that of the conventional lens and comprising a plurality of lenses in order to make compact the size of the entire copying machine and the projection lens system is endowed with a transmitting action which renders a part of an object to be projected upon individual lenses into a part of a corresponding image, whereby the entire lens system forms the projected image of the entire object on the plane of projection.
U.S. Pat. Nos. 3,584,952 and 3,592,542 disclose projection devices in which a plurality of lens systems are arranged along the lengthwise direction of a slit portion and a band-like area of an original to be copied is projected upon a photosensitive medium as a composite of partial images by these lens systems to thereby form an entire image. By making the lenses into an ommateal lens, the effective diameter of each lens is reduced and the conjugate corresponding to the same angle of view is shortened, thus rendering the entire device compact. That is, the projection device disclosed in the aforementioned U.S. Pat. No. 3,584,952 comprises three lenses in the direction of the optic axis, namely, front, intermediate and rear lenses, so that an intermediate image of a part of the original is formed on the intermediate lens disposed between the front lens and the rear lens by the front lens and this intermediate image is formed as the final image on the photosensitive medium by the rear lens. This intermediate lens functions as a field lens and has nothing to do with the original projecting action. However, this field lens has an important character in that it maintains uniform the brightness of the projected image formed on the photosensitive medium. Likewise, the projection device disclosed in the aforementioned U.S. Pat. No. 3,592,542 comprises three sets of two lenses, namely, two front lenses, two intermediate lenses and two rear lenses. In this device, three (or three sets of) lenses are disposed in the direction of the optic axis and it is difficult to set or otherwise adjust these lenses without eccentricity.
British Pat. No. 954,629 (complete specification issued on Apr. 8, 1964) discloses a lens having a great length in the direction of the optic axis thereof as compared with the effective diameter thereof.
However, the lens disclosed in this British patent is not a telecentric lens system, nor of the type in which an intermediate image is formed between a first lens and a second lens, nor of the type in which a predetermined distribution of intensity of light on the plane of projection is controlled. The lens described in the British patent is of the type in which the image of a part of an object is projected by a single lens system and this patent does not disclose that the images of individual parts are synthesized by a lens system array construction.
Japanese Patent Publication No. 30787/1970 shows an example of the projection lens system in which part images are synthesized by a lens system array and which adopts a telecentric arrangement. However, this projection lens system is an ordinary lens system and not a lens having a great length in the direction of the optic axis thereof as compared with the effective diameter thereof.
Our copending U.S. Application Ser. No. 889,404 discloses a construction having array-like projection optical systems each comprising a plurality of lenses, each of the projection optical systems having a first and a second lens so that an intermediate image of a part of an original is formed between the first and the second lens, each of the first and second lenses having a considerably great length in the direction of the optic axis as compared with the effective diameter thereof, the first lens being an emergence side telecentric system and the second lens being an incidence side telecentric system. Where such a lens system is applied to a copying machine or the like, it is desired that there be no irregularity of exposure and the present invention intends to meet such desire.
Optical fiber (tradename: Cellfock) having such an image forming action that the refractive index gradually decreases from the radially central portion thereof toward the marginal portion thereof is known from Japanese Patent Publication No. 28058/1972, etc., but the bar lens according to the present invention is such that the refractive index is uniform throughout the entire lens.